The invention relates to a method and apparatus for processing video pictures, especially for false contour effect compensation.
More specifically the invention is closely related to a kind of video processing for improving the picture quality of pictures which are displayed on matrix displays like plasma display panels (PDP) or display devices with digital micro mirror arrays (DMD).
Although plasma display panels are known for many years, plasma displays are encountering a growing interest from TV manufacturers. Indeed, this technology now makes it possible to achieve flat color panels of large size and with limited depths without any viewing angle constraints. The size of the displays may be much larger than the classical CRT picture tubes would have ever been allowed.
Referring to the latest generation of European TV sets, a lot of work has been made to improve its picture quality. Consequently, there is a strong demand, that a TV set built in a new technology like the plasma display technology has to provide a picture so good or better than the old standard TV technology. On one hand, the plasma display technology gives the possibility of nearly unlimited screen size, also of attractive thickness, but on the other hand, it generates new kinds of artefacts which could damage the picture quality. Most of these artefacts are different from the known artefacts occurring on classical CRT color picture tubes. Already due to this different appearance of the artefacts makes them more visible to the viewer since the viewer is used to see the well-known old TV artefacts.
The invention deals with a specific new artefact, which is called xe2x80x9cdynamic false contour effectxe2x80x9d since it corresponds to disturbances of gray levels and colors in the form of an apparition of colored edges in the picture when an observation point on the matrix screen moves. This kind of artefact is enhanced when the image has a smooth gradation like when the skin of a person is being displayed (e. g. displaying of a face or an arm,etc.). In addition, the same problem occurs on static images when observers are shaking their heads and that leads to the conclusion that such a failure depends on the human visual perception and happens on the retina of the eye.
Two approaches have been discussed to compensate for the false contour effect. As the false contour effect is directly related to the sub-field organization of the used plasma technology one approach is to make an optimization of the sub-field organization of the plasma display panels. The sub-field organization will be explained in greater detail below but for the moment it should be noted that it is a kind of decomposition of the 8-bit gray level in 8 or more lighting sub-periods. An optimization of such a picture have, indeed, a positive effect on the false contour effect. Nevertheless, such a solution can only slightly reduce the false contour effect amplitude but in any cases the effect will still occur and will be perceivable. Furthermore, sub-field organization is not a simple matter of design choice. The more sub-fields are allowed the more complicated will the plasma display panel be. So, optimization of the sub-field organization is only possible in a narrow range and will not eliminate this effect alone.
The second approach for the solution of above-mentioned problem is known under the expression xe2x80x9cpulse equalization techniquexe2x80x9d. This technique is a more complex one. It utilizes equalizing pulses which are added or separated from the TV signal when disturbances of gray scales are foreseen. In addition, since the fact that the false contour effect is motion relevant, we need different pulses for each possible speed. That leads to the need of a big memory storing a number of big look-up tables (LUT) for each speed and there is a need of a motion estimator. Furthermore, since the false contour effect depends on the sub-field organization, the pulses have to be re-calculated for each new sub-field organization. However the big disadvantage of this technique results from the fact that the equalizing pulses add failures to the picture to compensate for a failure appearing on the eye retina. Additionally, when the motion is increasing in the picture, there is a need to add more pulses to the picture and that leads to conflicts with the picture contents in case of very fast motion.
Therefore, it is an object of the present invention to disclose a method and an apparatus which achieves an efficient false contour effect compensation without affecting the picture content and which is easy to implement.
It is embodied in the present invention an apparatus and method for the compensation of the false contour effect by utilizing a motion estimator which determines motion vectors for blocks of pixel data. The resulting motion vectors are utilized for re-coding the pixels of the block wherein in the re-coding step a step of shifting the sub-fields of pixels is included. The so calculated pixels of the block are used to display the picture instead of displaying the original pixel data. Thus, the general idea of the invention is to detect the movements in the picture (displacement of the eye focus area) and to spread the right sub-field pulses over this displacement in order to be sure that the eye will only perceive the correct information through its movement.
This solution based on a motion estimator has the big advantage that it will not add false information in the picture and, in addition, this solution is independent from the picture contents and also from the sub-field organization. Further advantages are, that the inventive method allows a complete correction of the false contour effect when the motion vector is well-known. Also the method is not dependent from the used addressing technique for the plasma display panel. With regard to the disclosed specific embodiment, when the addressing or the sub-field organization changes, there is only the need to re-calculate the different centers of gravity of the sub-fields but the algorithm remains unchanged.
Another important advantage is that the picture noise has no impact on the correction quality. The method according to the invention is simple to implement. There is no need of a big memory since it does not need any kind of LUTs like the pulse equalization technique.
Advantageously, additional embodiments of the inventive method are disclosed in the respective dependent claims.